These geometries are IPoint and ILineString.
IPoint
The creation of an instances uses an IDirectionPositionImpl object.
IPoint pt00 = geomFactory.CreatePoint(pos00);
ILineString
The creation of an instances uses a DirectPositionCollection object, which is composed of IDirectionPositionImpl object.
positions.Add(pos01);
positions.Add(pos21);
ILineString line0121 = geomFactory.CreateLineString(positions);
positions.Clear();